This disclosure relates to polyetherimides and compositions containing the polyetherimides, as well as their method of manufacture and articles formed from the polyetherimide compositions.
Polyetherimides (“PEIs”) are amorphous, transparent, high performance polymers having a glass transition temperature (“Tg”) of greater than 180° C. PEIs further have high strength, heat resistance, and modulus, and broad chemical resistance, and so are widely used in applications as diverse as automotive, telecommunication, aerospace, electrical/electronics, transportation, and healthcare.
One process for the manufacture of polyetherimides is by polymerization of alkali metal salts of dihydroxyaromatic compounds, such as bisphenol A disodium salt (BPA·Na2), with a bis(halophthalimide). The molecular weight of the resulting polyetherimide can be controlled in two ways. The first is use of a molar excess of the bis(halophthalimide) relative to the alkali metal salt of the dihydroxy aromatic compound. The second is the preparation of the bis(halophthalic anhydride) in the presence of a monofunctional compound to form an end-capping agent, such as phthalic anhydride. The phthalic anhydride reacts with a portion of the organic diamine to form a monohalo-bis(phthalimide). The monohalo-bis(phthalimide) serves as an end-capping agent in the polymerization step by reaction with phenoxide end groups in the growing polymer chains.
However, these approaches can suffer from several drawbacks. Use of excess bis(halophthalimide) leads to high levels of residual unreacted bis(halophthalimide) and to high levels or chlorine end groups after completion of polymerization. Use of a monofunctional reactant such as phthalic anhydride can produce an undesirable by-product, a bis(phthalimide) having no halo functionality, which is formed by imidization of the phthalic anhydride with the organic diamine. The presence of residual bis(halophthalimide), monohalo-bis(phthalimide) and bis(phthalimide) in the polyetherimide can degrade the properties and/or performance of the polyetherimides in some applications.
Thus, there remains a need in the art for methods for controlling the molecular weight of polyetherimides, in particular methods that allow the manufacture of higher molecular weight polymers having lower levels of residuals, including residual bis(halophthalimide) and bis(phthalimide). It would be a further advantage if the process resulted in reduced levels of residual chlorine and chlorine end groups. Moreover, if would be a still further advantage if properties such as melt flow, impact strength and the like were not significantly adversely affected compared to prior art polyetherimides.